This invention generally relates to photoresponsive imaging devices, and more specifically, the present invention is directed to layered photoresponsive, or photosensitive imaging members containing a semi-conductive layer. In one embodiment of the present invention there is envisioned a layered photoresponsive device comprised of a semi-conductive layer, a photogenerating layer, and a charge transport layer. The layered photoresponsive imaging members of the present invention can be incorporated into numerous imaging devices, including xerographic imaging systems, wherein there is formed on these members, for example, electrostatic latent images, which images can subsequently be developed, and transferred to a suitable substrate.
The formation and development of electrostatic latent images on the surface of photoconductive materials, referred to in the art as photoreceptors or photosensitive compositions, is well known. In these imaging systems, and in particular in xerography, the xerographic plate containing the photoconductive insulating member is imaged by uniformly electrostatically charging its surface, followed by exposure to a pattern of activating electromagnetic radiation, such as light, which selectively dissipates the charge in the illuminated areas of the photoconductive member causing a latent electrostatic image to be formed in the non-illuminated areas. This latent electrostatic image can then be developed with developer compositions containing, for example, toner particles and carrier particles, followed by subsequently transferring this image to a suitable substrate such as paper. Many known photoconductive members can be selected for incorporation into the electrostatographic imaging system including for example, photoconductive insulating materials deposited on conductive substrates, as well as those containing a thin film barrier layer of aluminum oxide situated between the substrate and the photoconductive member. The barrier layer is included primarily for the purpose of preventing charge injection from the substrate into the photoconductive layer upon charging, as charge injection could adversely affect the electrical properties of the photoreceptor compositions involved.
Examples of photoconductive members include those comprised of inorganic materials and organic materials, layered devices of inorganic or organic materials, composite layered devices containing photoconductive substances dispersed in other materials, and the like. An example of one type of composite photoconductive layer used in xerography is described for example, in U.S. Pat. No. 3,121,006, wherein there is disclosed finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. In one embodiment, the photoconductive composition is comprised of particles of zinc oxide uniformly dispersed in a resinous binder coated on a paper backing. Useful binder materials disclosed include those which are incapable of transporting for any significant distance injected charge carriers generated by the photoconductive particles. Accordingly, as a result the photoconductive particles must be in a substantially contiguous particle to particle contact throughout the layer for the purpose of permitting charge dissipation required for a cyclic operation. Thus, about 50 percent by volume of photoconductive particles is usually necessary in order to obtain sufficient photoconductor particle to particle contact for rapid discharge. These high photoconductive concentrations can result in destroying the physical continuity of the resin, thus significantly reducing the mechanical strength of the binder material.
Illustrative examples of specific binder materials disclosed in this patent include, for example, polystyrene resins, silicone resins, acrylic and methacrylic ester polymers, polymerized ester derivatives of acrylic and alpha-acrylic acids, chlorinated rubber, vinyl polymers and copolymers, and cellulose esters.
Other examples of other known photoconductive compositions include amorphous selenium, halogen doped amorphous selenium substances, amorphous selenium alloys, including selenium arsenic, selenium tellurium, selenium arsenic antimony, halogen doped selenium alloys, wherein the halogen is chlorine, iodine, fluorine, or bromine, present in amounts of 50 parts per million to about 1,000 parts per million; cadmium sulfide, and the like. Generally, these photoconductive materials are deposited on suitable conductive substrates, and incorporated into xerographic imaging systems for use as imaging members.
Recently, there has been disclosed layered photoresponsive devices comprised of photogenerating layers and transport layers, deposited on conductive substrates as described, for example, in U.S. Pat. No. 4,265,990, and overcoated photoresponsive materials containing a hole injecting layer, covercoated with a hole transport layer, a photogenerating layer and a top coating of an insulating organic resin, as described, for example in U.S. Pat. No. 4,251,612. Examples of photogenerating layers disclosed in these patents include trigonal selenium and various phthalocyanines, while examples of transport layers described include certain diamines dispersed in inactive polycarbonate resin materials. The disclosures of each of these patents, namely, U.S. Pat. No. 4,265,990 and U.S. Pat. No. 4,251,612 are totally incorporated herein by reference.
Additionally, there is disclosed in Belgium Pat. No. 763,540, an electrophotographic member having at least two electrically operative layers, the first layer comprising a photoconductive layer which is capable of photogenerating charge carriers, and injecting photogenerated holes into a continuous active second layer containing a transporting organic material which is substantially non-absorbing in the spectral region of intended use, but which is active in that allows the injection of photogenerating holes from the photoconductive layer and the transporting of these holes through the active layer.
Other representative patents disclosing layered photoresponsive devices include U.S. Pat. Nos. 3,401,116, 4,115,116, 4,047,949 and 4,081,274.
While the above-described photoresponsive devices are generally suitable for their intended purposes, there continues to be a need for improved imaging members, particularly layered members containing semi-conductive materials, photogenerating layers and transport layers, which devices not only generate acceptable images but which can be repeatedly used in a number of imaging cycles without deterioration thereof from the machine environment, or surrounding conditions. Additionally, there continues to be a need for improved layered imaging members containing transmissive semi-conductive layers, and improved binder compositions for the photogenerating layer, and/or charge transport layer. Furthermore, there continues to be a need for improved binder materials for layered devices containing generating layers and transport layers. Also, there continues to be a need for layered photoresponsive devices of improved mechanical strength which contain a semi-conductive ground plane layer. Improved layered photoresponsive devices wherein no adhesive layers are needed for binding the photogenerating layer to the substrate are also needed.